The Digital SCIF: Compartmentalizing Sensitive data with Access Gateway Enterprise Edition (SCIFNET)


A little over six months ago Citrix released the Netscaler VPX virtual appliance and I was immediately thrilled with the potential to create my own virtual lab using XenServer and internal Xen networks on the hypervisor for downstream hosts. What I noticed was that I could locate resources inside a hypervisor’s black network and make them available externally via a VIP or a secure tunnel via a VPN connection. This lead me to believe that a resource that is, for all intents and purposes, off the public internal network can live safely on this network and never be exposed to the corporate network giving administrators another layer to further compartmentalized sensitive data off of an internal network. The compartmentalizing of sensitive data made me think of a military/DOD term called “skiff” or more appropriately Sensitive Compartmentalized Information Facility or a more appropriate acronym, SCIF. With a SCIF, all access, work and manipulation associated with specific sensitive information occurs within the confines of a specific building. What I am proposing is that you can use an Access Gateway Enterprise Edition to grant access to specific resources following this same model providing secure access, accountability and ensure that the only way to get to that data is via a gauntlet of two-factor authentication, application firewalls and endpoint analysis prior to the 2nd level of policy based access to internal resources that are only accessed via this secure tunnel.

SCIFNET: (“skiff-net”)

Placing a VPN in front of resources is not necessarily new, while VPN’s are most commonly used for remote access, there are instances where an administrator will use a VPN to secure a wireless network or to provide secure access to sensitive information. What I will describe in this is the next level where not only access is restricted but how the AGEE can integrate with the existing identity management framework as well as provide extensive logging and policy based access providing a least privileged model on a per resource basis.

Why put my data in a SCIF?

Currently your internal network is protected either by a NATed firewall, internal ACL’s etc. More mature networks have already layered their services by specific networks placing Oracle servers in one Network, Web Servers in another, SQL Servers in still another network, etc. As the security screws get tightened year after year we find that segmenting our services to particular networks may not be enough. Imagine if a database resided on a server that was completely invisible to the internal network that did not even have a default gateway assigned to it? No MAC Address to show up in ARP tables? No ports exposed via a NESSUS/SATAN/SARA scan?

In the “glass-half-empty” world of IT Security there are two types of systems, compromised and being-compromised. In 2004, during a particularly heated security discussion I suggested that the only way we could truly secure our systems was to unplug them from the network. With the SCIFNET solution I am proposing, you create an internal Network on your XenServer or ESX Server that does not reside on the internal network. This means that all communications occurs on the bus of the Hypervisor which has gigabit level speeds available on it.

So your SQL Server and Web Server are living inside a hypervisor with no Default Gateway and no ability to route to your internal Network? Great job…now how do you make it available? Well, in an earlier blog I discussed my time working as a County health inspector and when I inspected a convenient store in a particularly bad neighborhood, the shop owner would open a barred window and ask the customer what they wanted, he would take the money and go and get the merchandise and the entire transaction occurred outside his store. In this scenario, his exposure and risk was limited as the person was never allowed to enter the store and potentially rob him or attempt to leave with merchandise he/she did not pay for. SCIFNET works in a similar fashion where by the user connects to an Access Gateway who has a leg in both Networks but unlike a door, it is more like a barred window granting access to internal resources. But even better than my shop owner, I will log each access, I will account for how long they used the resource and I will log all un-authorized access attempts to this resource as well. By inserting a VPX in front of the resource, I am able to provide barred window access to sensitive resources that includes the highest level of accountability and record keeping.

Barred Window Access:

The Netscaler VPX provides for several secure access solutions to ensure anyone entering the secured network passes several forms of authentication, endpoint analysis and application firewall rules. Through each of these, before they even begin to attempt to access internal resources, they are met with a myriad of rules and scans to ensure they are allowed to even attempt access to sensitive data. While I may locate a resource on an internal Network on my hypervisor, I can offer it to the end user in a variety of ways among them via VPN or via AAA Authentication to a VIP. So while my web-server/db-server combo may exist on a completely invisible network inside a hypervisor, I am able to deliver it by creating a VIP on the VPX and offering that VIP to users on the internal Network. I can add a layer of security by forcing AAA Authentication to that VIP as of version 9.x of the Netscaler. If you need to grant non http access to a server that has either sensitive documents or a back end database you can offer a VPN tunnel into the internal network on the hypervisor. With split tunnel turned off, you can ensure that the client is only able to access internal resources while connected to the VPN and keep any outside connections from getting in.


As with the hardware appliance, the VPX allows for two factor authentication using smart cards(HSPD-12), SecurID, LDAP(AD/NDS/eDirectory) and local Authentication. All AAA logs can be sent to an event correlation engine for parsing and accountability to ensure that access attempts are accounted for and breach attempts can be reported and acted on immediately(Custom solution, email me if you are interested in it). Currently, I tested two factor authentication with AD Credentials and SecurID tokens and have used Smart Cards (CAC) Cards in a single authentication mode without any issues.

Endpoint Analysis:

In addition to authenticating users who wish to access sensitive data, you can also set minimum standards of the systems accessing the data. Using the VPX, you can ensure that systems accessing the SCIF have adequate virus signatures, host based firewalls and encryption software. Using Endpoint Analysis, you can ensure that any system meets a pre-selected set of requirements prior to accessing the systems inside. This will ensure that an infected system or a system that possesses an outdated virus signature is not allowed access. You may also only want a select group of systems accessing the SCIF, by putting a watermark in the registry. By scanning for this specific watermark, you can further restrict the number of systems that are allowed access in addition to the number of users.

Application Firewall:

Not everyone purchases this feature, in fact Citrix does not bundle this with the Express edition of the VPX but you can get a 90 day platinum edition that has it. What the application firewall does is allow your front end SSL VPN solution to be protected by a layer 4-7 firewall. By enforcing a “START URL” rule you can ensure that anyone who attempts to access the system by IP is dropped meaning any worm that is on the loose or person looking for port 443 or port 80 over an IP will not be able to access the authentication page. This same solution provides for Buffer Overflow, SQL Injection, Cross-Site Scripting and Custom based URL filter protection. An individual would need to know the exact URL to connect to before they even get a chance to Authenticate and be scanned.

Accessing Sensitive Resources:


Okay, you have typed in the correct URL, you have all of the necessary virus updates and watermarks to pass endpoint analysis and you have passed the two factor authentication, now you are free to access whatever you want inside the SCIF correct? No, in fact you have only entered the building, now the actual compartmentalized access control begins to take shape. While most SSL VPN Solutions will offer a similar gauntlet to logging in, once you are in the door, you can attempt to get to any IP address thereafter. The 2nd part of this posting has to do with what can be done after you have authenticated to ensure a user just doesn’t wander around the network looking for vulnerable systems. There are 3 parts to setting this up, Active Directory groups, Authorization Policies and the resources themselves.


Resources are defined by IP Address, Network ID and Port. For example, we have a database server that we want to allow a non-web based front end application to connect to. You create an internal Network on the XenServer where you want that resource to go than place the Virtual Machine on the XenServer and assign it to that network. The resource is accessed via the VPX who has a leg in both networks and bridges you from your internal network to the resource. Resources are defined to the AGEE via the Authorization Policy as an IP Address, Network and port. So my SQL Server that I have placed in (Already configured) with an IP Address of will be the resource I grant access to.

Authorization Policies:

This is the hierarchy for setting up access, AD Groups are assigned Authorization policies and Authorization policies have resources instantiated as rules. Using the resource above I would create an Authorization policy called “Sensitive DB” and assign the network ID or IP Address and port to that specific policy. You can assign more than one resource to an authorization policy. Once this is done, you can assign the policy to a group which brings us to the Active Directory integration with the AGEE.

Active Directory Group Extraction:

On the AGEE you will create a group that matches, exactly, the name of the group in Active Directory. This process is LDAP extraction so the same should work for eDirectory/NDS, iPlanet/SunOne and openLDAP. So let’s say for the example above we create an AD Group called “SensativeDB”. I create that exact same group on the Netscaler and so log as the user authenticates via Active Directory, the AGEE will check for matching LDAP groups. By assigning an Authorization Policy to a specific group, you can ensure that your access control to the sensitive information is still managed by the incumbent identity management framework and you also ensure that only users in specific groups are given access to sensitive data. The AGEE will act as the doorman ensuring that no one gets access to any area’s they are not supposed to.

Can I add access to resources outside of the SCIF?

Yes, if an outside resource on a different network needed to be made available to you while you were working inside the SCIF than you could accomplish this using the AGEE by setting up a VIP. If you were connected via VPN to the SCIF network (say and there was some reference data located on another network than you could create a VIP on the network and present external data to the inside with the same security gauntlet that you would present VIP’s to the internal Network. Say you had a group of contractors that you wanted to restrict to a SCIFNET but they also needed access to a web-based time keeping application, you could create an internal VIP and present it to the users inside the SCIF without exposing the entire internal network.

Integrating SCIFNET with VDI:

Initially, I wanted a similar situation as with a SCIF where a person walks into a room and accesses a secure terminal and from there you can access sensitive data on a network. In this manor, I can ensure that the end user is accessing data from what amounts to a glorified dumb terminal. Placing the VDI environment inside the SCIF created some federated services challenges that I have not mastered yet. Namely, you need AD to use XenDesktop and this meant poking a hole to allow for that AD integration. Also, with Endpoint Analysis and the “Barred Window” access offered by AGEE I felt the risk was mitigated. With Split Tunneling off and only allowing VPN traffic once the user connects to the AGEE I felt like we would be pretty safe. Also, you can still use VDI just one on your incumbent internal network instead of inside the SCIF. Otherwise, you need to set up a completely new AD Infrastructure inside the SCIF. I am not well versed enough with ADFS or some of the solutions to be able to adequately address this in this paper.

Can this be done without using a black network or VM’s:

It is likely more experienced readers have already made the connection to this and realized that yes it can be done. For Federal Government Sites, I would recommend putting a Netscaler 9010 with a FIPS module on the Network than set up an entire switched network that is NOT on the internal network but bridged by the AGEE software on the Netscaler. You can still deliver “barred window” access to the physical resources and you do not have the risk of the hypervisor itself becoming compromised. In production, it may be a lot harder to get the VPX based solution approved by security personnel but physically segmenting your resources may be easier to get approved and while I have not seen it in my environment I am quite sure a similar solution currently exists using either PIX or IOS based ACL’s.

Logging and Accountability:

What I like the most about using the AGEE for compartmentalized access is the logging. While a PIX or IOS based ACL will give you an offending IP. Currently, my VPN logs, once parsed and written to SQL, have the userID in addition to the port, source and destination IP Address. This means that I can type the IP Address of a resource into my SQL Reporting Services website and get the date, time, external IP, port and username of every single user who has accessed that resource. Additionally, the AGEE logs policy hits weather they are ALLOWED or DENIED. Once finished parsing, I can, on an hourly, daily or monthly basis check for users who trip the “DENIED” policy. Since I already have the username in my logs, I don’t have to hunt down who had what IP Address. This places me in a position to be more proactive, if I see a large number of ACCESS DENIED logs, I can go in and immediately kill a user’s VPN Session post haste. This also provides the opportunity to log access by user ID. The Digital Epidemiology portion is a whitepaper itself but having a user ID tied to each log makes incident response much faster.


You have a key resource at that must have a blanket “Deny” applied to it and is only available via exclusive “Allows”. For this you can create an Authorization policy called “TopSecret” and you create a rule for DESTIP== with an Action of DENY. You bind this policy to your AD Group and you set it higher than any other policy. This will ensure that if they attempt to get to that server, they will be denied access. What I like about the AGEE logs is that I get a username and the policy that was violated as well as the sourced IP Address. Effective parsing of these log files will allow for you to use event correlation to find out who has attempted to make unauthorized access.

 Example Log file from blocked access:

15:16:39     01/03/2010:20:15:40 GMT ns PPE-0 : SSLVPN NONHTTP_RESOURCEACCESS_DENIED 1250215 : Context jsmith@ – SessionId: 15- User jsmith – Client_ip – Nat_ip “Mapped Ip” – Vserver – Source – Destination – Total_bytes_send 298 – Total_bytes_recv 0 – Denied_by_policy “TopSecret” – Group(s) “CITGO VPN Testers”

While many segmented networks will have PIX logs that will give you this information, what I like about these logs is that I can parse them into a database and put each item marked red into a column for date/time, action, context, policy so in my database a query would return the following:

Time Context Destination Policy Action


jsmith@ TopSecret DENIED


In this scenario, I can immediately ask jsmith why he/she is trying to access this system. I have a record of the breach attempt and can even configure KIWI to alert me via Email at the exact time the breach occurs.

Likewise, with the AGEE I have a record of the successful attempts as well.

17:13:10    01/03/2010:22:12:10 GMT ns PPE-0 : SSLVPN TCPCONNSTAT 1299232 : Context jsmith@ – SessionId: 16- User jsmith – Client_ip – Nat_ip – Vserver – Source – Destination – Start_time “01/03/2010:22:12:10 GMT” – End_time “01/03/2010:22:12:10 GMT” – Duration 00:00:00 – Total_bytes_send 48 – Total_bytes_recv 19 – Total_compressedbytes_send 63 – Total_compressedbytes_recv 39 – Compression_ratio_send 0.00% – Compression_ratio_recv 0.00% – Access Allowed – Group(s) “CITGO VPN Testers”

Note that you do not get a policy named with the log, however all Deny’s should have the policy that denied them.


I plan to include some videos on how to accomplish this, it is relatively simple. This is also not a new concept and networks use IOS based ACL’s to accomplish this but I believe the AGEE be it as a Virtual appliance or physical hardware, provides a much easier solution than an enterprise NAC endeavor. In fact, I have heard some horror stories regarding NAC deployments. In the interim, while NAC continues to mature and organizations ease into their NAC solutions, SCIFNet allows you to perform the same security levels without taunting specter of an enterprise NAC deployment. Compartmentalize sensitive data and place an AGEE in front of it and you have all of the same benefits of Network Access Control at a fraction of the price and overhead.

 To see a video of SCIFNET put to use with a VPX and an internal XenServer Network click here:

Thanks for reading



One response

  1. […] ALL traffic that emerges from this machine be directed through the tunnel, effectively making the VPN gateway at the corporate side the default gateway of this machine at home.  The corporate firewall then is still protecting this […]

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